AlxGa1-xAs (x = 0-0.1) (111)A n(+) substrates have been polished with a solution composed of H2O, sodium hypochlorite (NaClO), acetic anhydride [(CH3CO)(2)O], and potassium hydroxide (KOH). The polished surface features, abrasion rate, and pH have been investigated as a function of (CH3CO)(2)O and KOH concentration. The solution composition providing optimum polished surfaces is NaClO (available Cl content > 5%) 0.25 dm(3), (CH3CO)(2)O 0.13 mol, and KOH 3.0 x 10(-4) mol in H2O 1 dm(3). At this composition the abrasion rate is 15 nm/min and the pH is 6.0. The roughness (rms value) of this optimum polished surface is 0.2 nm and atomically flat compared with commercially available GaAs (111)A substrates whose roughness is larger than 1.0 nm. The roughness changes of AlGaAs (111)A n(+) substrates prepared using the H2O-NaClO-( CH3CO)(2)O-KOH Solution and commercially available GaAs (111)A substrates following chemical cleaning using alkaline solution and subsequent treatment using HCl aqueous solution were measured. The roughness almost remains constant in n(+) AlGaAs (111)A. On the other hand the roughness decreases 26% in commercially available n(+) GaAs (111)A.